Network vulnerability scanners are capable of *probing a wide range of network-connected devices* for known vulnerabilities. They reach out to any systems connected to the network, attempt to *determine the type of device and its configuration*, and then *launch targeted tests* designed to detect the presence of any known vulnerabilities on those devices. The following tools are examples of network vulnerability scanners: - *Tenable's Nessus* is a well-known and widely respected network vulnerability scanning product that was one of the earliest products in this field. - *Qualys's* vulnerability scanner is a more recently developed commercial network vulnerability scanner that offers a unique deployment model using a software-as-a-service (**SaaS**) management console to run scans using appliances located both in on-premises data centres and in the cloud. - Rapid7's *Nexpose* is another commercial vulnerability management system that offers capabilities similar to those of Nessus and Qualys. - The open source *OpenVAS* offers a free alternative to commercial vulnerability scanners. Many organisations choose to deploy two different vulnerability scanning products in the same environment as a **defence-in-depth control**.